Switched-Capacitor Converters (SCC) are preferred over inductor based switch-mode regulators in low power applications, when the application calls for small size and if the electromagnetic field radiated from the switched inductor may pose a problem. Therefore, SCC are popular in power management of mobile devices where the electromagnetic interference could be a problem and small size is a must. However, SCC suffer from a fundamental power loss deficiency that make their use in some applications prohibitive. The power loss is due to the inherent energy dissipation when a capacitor is connected to a voltage source or another capacitor that have different voltage from the capacitor's voltage (before the interconnection). Theory predicts that this power loss is proportional to (ΔV)2 where ΔV is the voltage differences before connection. As a result, SCC will exhibit a rather high efficiency if, during the switching cycle, the capacitors are connected to voltages (power sources and other capacitors) that have a similar voltage to the voltage across said capacitor. It is thus a well known phenomenon that when SCC are operated around the target conversion ratio (input to output voltage), the efficiency will be high and may exceed 90%. But when the same SCC is operated at a different conversion ratio, the efficiency drops dramatically. This is due to the fact that in the target ratio the capacitors do not see appreciable voltage variations. In practical applications one would expect the operational input to output voltage conversion ratio to change and hence there is no way to escape the losses in the prior art SCC in which the ‘target’ conversion ratios are limited to one or several conversion ratio values which are spread apart. For example, Linear Technology's (CA, USA) SCC LTC1999 can be configured for target input to output conversion ratios of 1/2 and 2/3 and hence at these ratios the efficient is relatively high. However, in between and outside this conversion ratio the efficiency drops dramatically.
The inherent loss mechanism in prior art SCC is a severe limitation considering the importance of high efficiency in general and in mobile equipment in particular since it shortens the battery life.
Thus there is a need for and it would be highly advantageous to have a SCC design that will have target conversion ratios that are spaced at high resolution over the range of interest and thereby improve the efficiency of the power management systems.